Applications Of EM Waves In Broadcasting Technology Computer Science Essay

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Abstract- This document is the term paper about the uses of EM waves in the broadcasting technology. The document is an amalgamation of the introduction to EM waves, their basic properties, and the uses in broadcasting technology. The basic spheres of broadcasting technology, where EM waves are most used, are explained.

Keywords- EM waves, characteristics, propagation, Tabulated data, radio communication, Television casting, webcasting.

INTRODUCTION

Electromagnetic waves are formed when an electric field couples with a magnetic field. The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. The aspects of these waves are covered in the electromagnetic radiation spectrum, also called as electromagnetic radiations or electromagnetic spectra.[1] Also, Electromagnetic radiation can be described in terms of a stream of photons, which are mass less particles each travelling in a wave-like pattern and moving at the speed of light. Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. [2]

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Fig 1: Electric and Magnetic fields are mutually perpendicular

In ELECTROMAGNETIC waves, electric and magnetic field components oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation.

Fig 2: different regions of EM spectra

Electromagnetic radiation is emitted from all matter with a temperature above absolute zero. Temperature is the measure of the average energy of vibrating atoms and that vibration causes them to give off electromagnetic radiation. As the temperature increases, more radiation and shorter wavelengths of electromagnetic radiation are emitted. Microwaves, radio, and television waves are emitted from electronic devices. Sparks and alternating current cause vibrations at the appropriate frequencies. [3]

CHARACTERISTICS OF EM WAVES

Electromagnetic waves are transverse waves, similar to water waves in the ocean or the waves seen on a guitar string. This is as opposed to the compression waves of sound. In Wave Motion, all waves have amplitude, wavelength, velocity and frequency. [4]

AMPLITUDE

The highest possible displacement of any wave particle above its mean position is the amplitude of the wave. There are different criteria of measurement of the wave amplitude of the electromagnetic waves. The reason behind this is the fact that electromagnetic spectra are vast region spectra. As such it has different forms of waves; hence, different approaches have to be adopted.

With visible light, the brightness is usually measured in lumens. With other wavelengths the intensity of the radiation, which is power per unit area or watts per square meter is used. The square of the amplitude of a wave is the intensity.

WAVELENGTH

The wavelengths of electromagnetic waves vary from extremely long to extremely short. The reason behind this thing, as already stated above, is the wide range spectra of the electromagnetic waves. The wavelengths determine how matter responds to the electromagnetic wave, and those characteristics determine that particular group of wavelengths.

The behaviour of electromagnetic radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When electromagnetic radiation interacts with single atoms and molecules, its behaviour depends on the amount of energy per quantum it carries.

VELOCITY

The velocity of electromagnetic waves in a vacuum is approximately 3*108 meters per second, the same as the speed of light. When these waves pass through matter, they slow down slightly, according to their wavelength. This is because 3*108 is the speed in vacuum. When the measurement criteria comes to measurement in some media, the media is denser than vacuum. So, speed slows down.

FREQUENCY

The frequency of any waveform equals the velocity divided by the wavelength. The units of measurement are in cycles per second or Hertz. Same as the case with wavelength, the frequencies of different EM waves is scattered over a wide range of values due to their variety of types.

PROPAGATION OF EM WAVES

Electromagnetic waves are waves which can travel through the vacuum of outer space. Electromagnetic waves are created by the vibration of an electric charge. This vibration creates a wave which has both an electric and a magnetic component. The mechanism of energy transport through a medium involves the absorption and reemission of the wave energy by the atoms of the material. When an electromagnetic wave impinges upon the atoms of a material, the energy of that wave is absorbed. The absorption of energy causes the electrons within the atoms to undergo vibrations. After a short period of vibrational motion, the vibrating electrons create a new electromagnetic wave with the same frequency as the first electromagnetic wave. While these vibrations occur for only a very short time, they delay the motion of the wave through the medium. Once the energy of the electromagnetic wave is reemitted by an atom, it travels through a small region of space between atoms. Once it reaches the next atom, the electromagnetic wave is absorbed, transformed into electron vibrations and then reemitted as an electromagnetic wave. The actual speed of an electromagnetic wave through a material medium is dependent upon the optical density of that medium. Different materials cause a different amount of delay due to the absorption and reemission process.

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From its origin, the wave will propagate outwards in all directions. If the medium in which it is propagating (air for example) is the same everywhere, the wave will spread out uniformly in all directions.

The given figure below shows the wave propagating in all the directions uniformly. This happens in a homogenous medium. The wave propagates outwards from the centre. It will spread out enough that it will appear to have the same amplitude everywhere on the plane perpendicular to its direction of travel. This is a plane wave, ideally travelling [5]

 Fig 3: EM waves propagating in all directions

TABULATED FORM OF EM WAVE SPECTRA

Wave

Wavelength

Use

Long Wave Radio

1500 m

Broadcasting

Medium Wave Radio

300 m

Broadcasting

Short Wave Radio

25 m

Broadcasting

FM Radio

3 m

Broadcasting and communication

UHF Radio

30 cm

TV transmissions

Microwaves

3 cm

Communication

Radar

Heating up food

Infra red

3 mm

Communication in optical fibres

Remote Controllers

Heating

Light

200 - 600 nm

Seeing

Communicating

Ultra violet

100 nm

Sterilising

Sun tanning

X-ray

5 nm

Shadow pictures of bones

Gamma rays

<0.01 nm

Scientific research

Considering the above table, we can infer that EM waves occupy a huge area of the spectral region, and they have wide variety of uses. It is impossible to neglect the importance of EM waves in various scientific, medical, practical and other important fields like communication etc. The practical usage of the EM waves in the broadcasting technology would be discussed in the coming topics, as per the topic of the term paper.

USES OF EM WAVES IN BROADCASTING TECHNOLOGY:

Broadcasting is made up of two words- broad + casting. Broad means wide, casting means to send. Hence, broadcasting refers to sending any signal over a wide area. Broadcasting is the process, by which a single or multiple stations send or transmit signals to a wide area.

Basically, broadcasting of any signal takes place through various channels. There is a broadcasting station at one end, and at the other end, there is receiver. In between these two ends, there are various intermediate stages like amplification stations, transmitting stations, satellites, antennas etc. A brief block diagram of the broadcasting process through a satellite is as given below.

Fig 4: block diagram of radio broadcasting system

In the above diagram, the ground station is too far from the receiving stations. Hence, it casts the signal to the broadcasting satellite, which in turn broadcasts it to the receiving stations.

DIFFERENT APPLICATIONS OF EM WAVES IN BROADCASTING TECHNOLOGY:-

Radio Communications

Television broadcasting

Cellular broadcasting

Internet Broadcasting (Webcasting)

OFC broadcasting

Satellite Communication

RADIO BROADCASTING-

Radio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, phase, or pulse width. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

Radio broadcasting is an audio (sound) broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and, thus, to a receiving device. Audio broadcasting also can be done via cable FM, local wire networks, satellite and the Internet. The best known type of radio stations are the ones that broadcast via radio waves. These include foremost AM and FM stations.

As given in the adjoining picture, there are various channels of radio broadcasting. The transmitting stations transmit the signals to the antenna, which in turn transmits it further to different nodes, antennas and through various amplification and repeater stations, and then finally to the receiving station.

The radio signals are transmitted as EM waves. These waves are of various types as AM, FM, SW, MW etc.

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AM stations were the earliest broadcasting stations to be developed. AM refers to amplitude modulation, a mode of broadcasting radio waves by varying the amplitude of the carrier signal in response to the amplitude of the signal to be transmitted. One of the advantages of AM is that its unsophisticated signal can be detected (turned into sound) with simple equipment. If a signal is strong enough, not even a power source is needed; building an unpowered crystal radio receiver was a common childhood project in the early years of radio. Another advantage to AM is that it uses a narrower bandwidth than FM. AM radio is confined to a band from 535 kilohertz to 1,700 kilohertz. FM refers to frequency modulation, and occurs on VHF airwaves in the frequency range of 88 to 108 MHz

Fig 5: A reprensating diagram of different blocks of a radio broadcasting system

Radio systems used for communications need to have the following elements. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The mostly used oscillators are colpit oscillators. The transmitter contains a system to modulate (Modify) some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna. This structure converts the rapidly-changing alternating current into an electromagnetic wave that can move through free space.

Electromagnetic waves travel through space either directly, or have their path altered by reflection, refraction or diffraction. The intensity of the waves diminishes due to geometric dispersion. Some energy may also be absorbed by the intervening medium in some cases. Noise will generally alter the desired signal. This electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators. Noise is also produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough, the desired signal will no longer be discernible; this is the fundamental limit to the range of radio communications.

The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is "tuned" to respond preferentially to the desired signals, and reject undesired signals.

Early radio systems relied entirely on the energy collected by an antenna to produce signals for the operator. Radio became more useful after the invention of electronic devices such as the vacuum tube and later the transistor, which made it possible to amplify weak signals. Today radio systems are used for applications from walkie-talkie children's toys to the control of space vehicles, as well as for broadcasting, and many other applications. [7]

A new entry into the segment of the radio broadcasting is the SATELLITE radio. This type of radio is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals. Satellite radio offers a meaningful alternative to ground-based radio services

Local repeaters similar to broadcast translator boosters enable signals to be available even if the view of the satellite is blocked, for example, by skyscrapers in a large town. Major tunnels can also have repeaters. This method also allows local programming to be transmitted such as traffic and weather in most major metropolitan areas.

DIFFERENT STAGES IN RADIO BROADCASTING

There are two principal ways in which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna. One way is by ground waves and the other is by sky waves. Ground waves are radio waves that travel near the surface of the Earth (surface and space waves). Sky waves are radio waves that are reflected back to Earth from the ionosphere.

Fig 6: Difference b/w a Sky Wave and a Space wave

In order to broadcast radio, the signals pass through various stages. These are highlighted as under:

The first one is the broadcasting station. It is station for the production and transmission of AM or FM radio broadcasts. The signals are produced and transmitted to the further stages. These stages have the means to produce, prepare, amplify, modulate and transmit the signals.

Then further, the signal is transmitted to the antenna. An antenna (or aerial) is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic radiation into electrical current, or vice versa. Antennas generally deal in the transmission and reception of radio waves, and are a necessary part of all radio equipment. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, cell phones, radar, and spacecraft communication. Antennas are most commonly employed in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.

Physically, an antenna is an arrangement of one or more conductors, usually called elements in this context. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals. Some receiving antennas (such as parabolic and horn types) incorporate shaped reflective surfaces to collect the radio waves striking them and direct or focus them onto the actual conductive elements.

A common antenna is a vertical rod a quarter of a wavelength long. Such antennas are simple in construction, usually inexpensive, and both radiate in and receive from all horizontal directions. One limitation of this antenna is that it does not radiate or receive in the direction in which the rod points. Typically, antennas are designed to operate in a relatively narrow frequency range. The design criteria for receiving and transmitting antennas differ slightly, but generally an antenna can receive and transmit equally well. [8]

Fig 7: A Radio Antenna in NASA, USA.

Finally, these signals after passing through one or more antenna stations, it is received by the receiver, which we generally know as radio set. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate (change) some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly-changing alternating current into an electromagnetic wave that can move through free space (sometimes with a particular polarization (waves)).

Electromagnetic waves travel through space either directly, or have their path altered by reflection, refraction or diffraction. The intensity of the waves diminishes due to geometric dispersion (the inverse-square law); some energy may also be absorbed by the intervening medium in some cases. Noise will generally alter the desired signal; this electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators. Noise is also produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough, the desired signal will no longer be discernible; this is the fundamental limit to the range of radio communications.

The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is "tuned" to respond preferentially to the desired signals, and reject undesired signals.

RADIO FREQUENCY RANGE

Radio frequencies occupy the range from a few tens of hertz to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum. Other types of electromagnetic radiation, with frequencies above the RF range, are microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation.

OPTIC FIBER BROADCASTING

Fibre-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fibre. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fibre-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibres have largely replaced copper wire communications in core networks in the developed world.

An optical fibre is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. The fibre consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fibre, or gradual, in graded-index fibre.

The process of communicating using fibre-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fibre, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal. [9]

Fig 8: Passage of light through OFC.

WORKING OF A FIBRE OPTIC CABLE [10]

Fibre-optic relay systems consist of the following:

Transmitter - Produces and encodes the light signals

Optical fibre - Conducts the light signals over a distance

Optical regenerator - May be necessary to boost the light signal (for long distances)

Optical receiver - Receives and decodes the light signals

Transmitter

The transmitter receives and directs the optical device to turn the light "on" and "off" in the correct sequence, thereby generating a light signal.

The transmitter is physically close to the optical fibre and may even have a lens to focus the light into the fibre. Lasers have more power than LEDs, but vary more with changes in temperature and are more expensive. The most common wavelengths of light signals are 850 nm, 1,300 nm, and 1,550 nm (infrared, non-visible portions of the spectrum).

Optical Regenerator

As mentioned above, some signal loss occurs when the light is transmitted through the fibre, especially over long distances (more than a half mile, or about 1 km) such as with undersea cables. Therefore, one or more optical regenerators is spliced along the cable to boost the degraded light signals.

An optical regenerator consists of optical fibres with a special coating (doping). The doped portion is "pumped" with a laser. When the degraded signal comes into the doped coating, the energy from the laser allows the doped molecules to become lasers themselves. The doped molecules then emit a new, stronger light signal with the same characteristics as the incoming weak light signal. Basically, the regenerator is a laser amplifier for the incoming signal.

Optical Receiver

The optical receiver takes the incoming digital light signals, decodes them and sends the electrical signal to the other user's computer, TV or telephone. The receiver uses a photocell or photodiode to detect the light.

ADVANTAGES

Compared to conventional metal wire (copper wire), optical fibres are:

Less expensive - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire.

Thinner - Optical fibres can be drawn to smaller diameters than copper wire.

Higher carrying capacity - Because optical fibres are thinner than copper wires, more fibres can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into the cable TV box.

Less signal degradation - The loss of signal in optical fibre is less than in copper wire.

Light signals - Unlike electrical signals in copper wires, light signals from one fibre do not interfere with those of other fibres in the same cable. This means clearer phone conversations or TV reception.

Low power - Because signals in optical fibres degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.

Digital signals - Optical fibres are ideally suited for carrying digital information, which is especially useful in computer networks.

Non-flammable - Because no electricity is passed through optical fibres, there is no fire hazard.

Lightweight - An optical cable weighs less than a comparable copper wire cable. Fibre-optic cables take up less space in the ground.

CONCLUSIONS

This term paper is the perfect way of the representation of the importance of EM waves in the broadcasting technologies. Not only in this field, but in each and every field, EM waves are much important. It’s the EM waves which are a sole factor of our vision.

In the broadcasting field, it is impossible to work without the EM waves. The transmitted radio waves, of various types, are all the EM wave types. Difference is only in their physical attributes like wavelength, frequency etc.

The fibre optic cable, the most efficient way of broadcasting signals, is all dependent upon the EM waves, in the form of visible or infrared light. The OFC is the revolutionary mean of broadcasting. As such, the EM waves hold importance to really a great extent.

ACKNOWLEDGEMENTS

I would like to express my sincere thanks to all those who helped me in the completion of this term paper. My hearty acknowledgements go to Mr. Princejeet Singh for his valuable guidance. Then my thanks to my friends who helped me in some or the other way.